Microelectromechanical system (which may be abbreviated to “MEMS”) can fulfill various functions in wide-ranging fields such as wireless technologies, optical technologies, acceleration sensors and biotechnologies. MEMS, in particular, is favorably used in a device such as a switch and a filter for a wireless terminal.
As an information and communication device such as a wireless terminal is being in widespread use, a small-sized terminal that is accommodated to various communication systems is required. In addition, it is recently desired to downsize a passive component since there is a tendency of increase in the number of the passive components, such as a switch, which are built in a housing of the terminal.
A radio-frequency microelectromechanical system (RF-MEMS) switch, which is manufactured using a MEMS technology, is regarded as a favorable component to satisfy these demands. The RF-MEMS switch is a switch wherein a micro movable electrode is moved to mechanically switch a transmission path of a signal. The advantage of the RF-MEMS switch is excellent radio-frequency characteristics such as ultra-low insertion loss, high isolation, linearity and so on. Further, since the MEMS switch can be produced by a process compatible to a semiconductor, the MEMS switch can be built in an RF-IC. For these reasons, the development of the MEMS switch is expected to be a technology which significantly contributes to downscaling of the wireless segment.
The conventional RF-MEMS switch mechanically switches the transmission path of signal by contacting a membrane or bar movable body having a fixed-fixed beam construction or a cantilever construction with an electrode, or separating the movable body from the electrode. Many conventional RF-MEMS switches use electrostatic force as a source of driving force for the movable body. The RF MEMS switch wherein electromagnetic force is used as a source of driving force has been proposed.
There is a series-type switch as one type of the RF-MEMS switches. The series-type RF-MEMS has a movable electrode and a driving electrode. The movable electrode, which is a micro membrane with a length of several hundreds μm is located on extension of the signal line for transmitting an RF signal and is separated from a signal electrode. A tip of the movable electrode is open. The driving electrode is provided just beneath the region where the membrane of the movable electrode is not located. When a DC potential is applied to the driving electrode, the movable electrode is attracted to the driving electrode side by the electrostatic force, and then contacted with the signal line which outputs the signal. The short circuit is established between the signal lines and the RF signal is transmitted through the movable electrode (that is, “on” state is established). When the DC potential is not applied to the driving electrode, the movable electrode does not contact with the signal line and thereby the RF signal is blocked (that is, “off” state is established).
An example of a construction of the conventional series-type MEMS switch is described with reference to FIGS. 7 and 8. FIG. 7 is a top view showing an example of the conventional MEMS switch, and FIG. 8 is a cross-sectional view showing the A-A′ section in FIG. 7.
In the MEMS switch 500 shown in the figure, an insulating layer 509 is formed as an interlayer insulating film on a substrate 510, and a driving electrode 502 and a signal electrode 504 as the transmission path are formed on the insulating layer 509. A movable electrode 501, which has a contact electrode (membrane) 503 and is supported by a support 505, is provided such that the electrode 501 is opposed to and separated from the electrodes 502 and 504. The movable electrode 501 is a deformable member and formed on only one side when viewed from the contact electrode 503 (that is, the electrode 501 is a cantilever beam). The switch of this construction is made “on” by applying the electrostatic force between the movable electrode 501 and the driving electrode 502 to electrically contact the contact electrode 503 with the signal electrode 504.
Further, an electrostatic type relay is disclosed in Patent Document 1, as another embodiment of the microelectromechanical system switch. The switch disclosed in Patent Document 1 is of a construction wherein the movable electrode which is elastically supported is made into surface contact with a fixed electrode by the electrostatic force.